I have been using raspberry pi 3 model since last 1 year. My pi has been running 24x7 since past 7 months. I was working on it via SSH and suddenly it stopped working. Now when I connect it to power, it does not start. No LEDs turn on and it produce some humming sound. I change the power supply but I still face the same issue.
Please help.
Thanks in advance.

Where on the board is the humming coming from? Do you have a fan attached?
Try using a different SD card. I have had an RPi abruptly stop working because of a dead SD card.
If the CPU or other chips on your raspberry used to be continuously hot, then one of the chips may have failed.

I'm setting up a webpage and email server on a Pi 3B+ running Ubuntu Mate 18.10.
Please read the Unanswered topics section and help with whatever you can!

Where on the board is the humming coming from? Do you have a fan attached?
Try using a different SD card. I have had an RPi abruptly stop working because of a dead SD card.
If the CPU or other chips on your raspberry used to be continuously hot, then one of the chips may have failed.

Thanks Vinay.
I just discovered that one of the module attached to Pi, had damaged IC. Input pin of the module was generating 12V DC which was connected to one of the GPIOs on Pi, this might have damaged the Pi. Are there any chances that I can get it repaired or I will have to buy a new one?

I just discovered that one of the module attached to Pi, had damaged IC. Input pin of the module was generating 12V DC which was connected to one of the GPIOs on Pi, this might have damaged the Pi. Are there any chances that I can get it repaired or I will have to buy a new one?

No chance. It's dead. Very dead. (The GPIO inputs connect directly to the SOC.)